Radio frequency induction heating apparatus



1, 1943. J. J. MOREY 2,328,225

RADIO FREQUENCY INDUCTION HEATING APPARATUS Filed Dec. 6, 1940 3 Sheets-Sheet l INVEN TOR.

ATTORNEY.

I JAMES .J-MOREY 2:: JAMES J.MUREY i INVENTOR// Aug. 31, 1943. J. .J. MOREY 2,328,225

RADIO FREQUENCY INDUCTION HEATING APPARATUS Filed Dec. 6, 1940 3 Sheets-Sheet 2 co m 8 -a m 3 T r\ \J a Tiff ATTORNEY.

Aug. 31, 1943. J. J. MOREY 2,328,225

RADIO FREQUENCY INDUCTION HEATING APPARATUS Filed Dec. 6 1940 s Sheets-Sheet 5 JAMES J. MD RE Y INV EN TOR.

WWW

ATTORNEY.

Patented Aug. 31, 1943 UNITED STATES PATENT OFFICE RADIO FREQUENCY INDUCTION HEATING APPARATUS 2 Claims.

This invention relates to a new liquid coating drying process particularly adapted for use on metal surfaces covered with paint, lithographic ink, high volatile solvents, water and the like. Also for applying heat for the purpose of annealing or heating preparatory for hardening metal objects.

An object of this invention is to heat and/or dry metal articles by causing the articles to come in contact with an electromagnetic field at a radio frequency,

Another object of this invention is to provide a radio frequency induction heating apparatus that will dry a wet or coated metallic article in a few seconds which formerly required four hours, and without subjecting the covering material to an excess of uncontrolled heat. Another object of this invention is to provide means for conveying liquid covered metal articles to be dried through the effective area of an inductance coil having an induction field, and causing an electromagnetic coupling between the coil and the article being heated, which determines the heating action.

Another object of this invention is to provide in an induction heating apparatus, a centrally divided inductance coil having spaced-apart winding units integrally connected at the bottom of the coil and providing an open top passageway, in conjunction with an overhead conveyor located externally of the induction coil and designed so that articles comprising magnetic permeable metal to be heated may be moved transversely of the axis of the coil.

Another object of this invention is to provide, in combination with a radio frequency induction heating apparatus having a magnetic field of predetermined intensity, an overhead conveyor for supporting and moving coated metal articles through said field, and means for actuating the conveyor in timed relation with the time required to dry coatings on the metal articles.

Another object of this invention is to provide, in combination with a radio frequency induction heating apparatus comprising spaced-apart coaxial coils forming an open top passageway therebetween, the said coils being connected in series and winding in the same direction, a magnctic field of predetermined intensity in the said passageway, an overhead conveyor for supporting and moving coated metal articles through the central portion of the said field and transversely of the axis of the said coils, and means for actuating the conveyor in timed relation with the time required to dry coatings on the metal articles.

Another object of this invention is to provide in combination a heating chamber including a conveyor adapted for carrying coated metal articles, an induction coil having a small heating capacity and an induction coil of large heating capacity, the said coils being operatively positioned in the pathway of the conveyor to first preheat and then bring the said coating to a predetermined temperature in successive steps.

With the above and other objects in view, the invention will be hereinafter .more particularly described, and the combination and arrangement of parts will be shown in the accompanying drawings and pointed out in the claims which form part of this specification.

Reference will now be had to the drawings, wherein like numerals of reference designate corresponding parts throughout the several views, in which:

Figure l is a front elevation of the heating apparatus.

Figure 2 is a cross-sectional view, the section being taken as on line 2-2 in Figure 1.

Figure 3 is a diagrammatic representation of the elements of the invention and their electrical connection.

Figure 4 is a view of the apparatus shown in Figure 1, with the addition of a nozzle for conveying a. cooling liquid in a direction for quenching heat treated metal articles.

Figure 5 is a fragmentary view of modified quenching means comprising mechanism for forcing a portion of the conveyor and heat treated metal articles into a tank containing a cooling liquid.

In the illustrated embodiment of the invention, Figures 1 to 3 inclusive indicate a self contained apparatus for drying a liquid or coating upon a metal surface and which comprises a casing l0 having a heating chamber H, access to which may be had through an opening 12 in the front face of the casing.

As best shown in Figure 2, the heating chamber l I is open at its upper elevation so as to permit carrier arms 13 secured to links of a sprocket chain M to move in a path above and substantially parallel with the lower surface l5 of the chamber ll. Article supports I6, preferably of inverted T-shaped form have hooked upper ends in engagement with hooked lower ends ll of the carriers l3. The supports l6 are adapted to carry a plurality of metal articles 18 having coatings thereon to be heated to a predetermined temperature.

The sprocket chain i4 is mounted on a sprocket wheel l9 and on a driving sprocket wheel 20. The sprocket wheel I! is secured to a shaft 2| rotatably disposed within bearings 22. The bearings 22 are suitably mounted on a horizontal supporting surface 23. The driving sprocket wheel is secured to a drive shaft 24 rotatably disposed within bearings 25 mounted on the supporting surface 23.

The sprocket chain I4 is endless and with the carrier arms l3 extending all around the chain forms an endless travelling conveyor 30.

Mounted horizontally in the heating chamber H is an inductance coil 3| having a plurality of circular turns. The coil 3| has been formed to provide spaced-apart coaxial sections 32, 32. The turns in both of the sections wind in the same direction. by an intermediate part 33 which connects the said sections in series. The intermediate part 33 is positioned at the lower level of the sections 32 and a narrow open top passageway 34 is thus formed between the sections of the coil 3|.

As shown in Figure 1, the coated metal articles iii to be heated, are supported by the carrier arms i3 so as to pass through the axis of the coil sections when the conveyor is in operation and the articles 8 are in the passageway 34.

A single section inductance coil 35 having a plurality of circular turns has been mounted horizontally in the heating chamber H with its axis in parallel and considerably spaced relation from the axis of the coil 3|. the coil 35 has been placed in alignment with the passageway 34. The direction of motion of the coated metal articles I8 is arranged to cause the articles to first pass by the coil 35 which imparts to the coatings only a fraction of the necessary heat and to preheat the metal articles. The articles then pass through the coil 3| which imparts the full predetermined heat treatment to the articles.

The carrier arms l3 of the conveyor 30 are preferably made of insulating material to prevent magnetic flux from the inductor coil 3| from straying to the ferrous metal elements of the conveyor.

In the radio frequency circuit arrangement shown in Figure 3, three thermionic tubes are employed in the amplifier circuit, the filaments of these tubes being supplied with current through a step-down transformer 4| from an A. C. supply circuit through leads 43 and 44.

A step-up transformer 42 having a high voltage secondary winding 45, is used for feeding the plates of two rectifying tubes 46, 46. The two ends of the secondary winding 45 are connected to the plates of the rectifier tubes in order to utilize both halves of the alternating current frequency input cycle.

The step-down transformer 4| comprises two independent secondary windings 41 and 48. The winding 41 is wound to supply current at a lower voltage to the filaments of the tubes 40, while the winding 48 is a three-wire balancing winding, the middle leg 49 being the common return. The ends of the winding 48 are used to supply filament heating voltage of the rectifying tubes.

A radio frequency choke coil 50 has been connected in series with the positive high voltage return to prevent short circuiting the radio frequency voltage. A condenser 5| has been placed across the coil 3| and is the main tank condenser The sections 32 are joined together One end face of t used to predetermine the frequency and the power output of the device. A condenser 52 has been placed in the radio frequency plate lead 53 to the tank circuit to prevent the D. C. current from appearing on the inductor coil 3|.

A grid blocking condenser 54 has been placed in the grid return circuit. The grids of the tubes 40 are each connected through resistances 55, 56 and 51. The resistances 55, 56 and 51 are parasitic suppressor resistors used to eliminate ultra high frequency parasitics which occurs when tubes are operated in parallel. The numeral 58 also indicates a master parasitic suppressor. The numeral 59 indicates a grid biasing resistor. The numeral 60 indicates a meter used to read the grid current drawn by the tubes 40. The numeral 6| indicates a meter for reading the plate current drawn by the tubes 40. In operation filament switch 53 is closed first and then plate voltage switch 54 is closed to supply the necessary plate voltage.

A resistor combination provides a balanced center tap or common return. By-pass condensers 66 prevent radio frequency feeding into the filaments from the condensers.

The means for actuating the conveyor 30 in timed relation with the time required to heat the coated metal articles I8, comprises a motor 10 which is connected by a V-type belt H to a variable speed transmission 12. The transmission 12 comprises two pulleys 13, 13, mounted side by side on a shaft 14, and a shiftable intermediate member 15 which is mounted on shaft 14 and which is common to both pulleys 13. A V-type belt 16 connects the variable speed transmission 12 with a geared speed reduction device "l1, which is well known in the art. A rod 19 is secured at one end to one of two arms 80, 80, by means of which the variable speed transmission is actuated. The arms are pivotally mounted on a pedestal (not shown). The variable speed transmission 12 is in the form shown and described in Patent No. 2,035,269. By manually adjusting a handle 8| at the forward end of the rod 19, the operator swings the arms 80 and causes swinging motion of the pulleys 13 to the right or to the left and obtains the desired speed reduction from the motor 10 to the conveyor drive shaft 24. The speed of the conveyor drive shaft 24 and the speed of the conveyor 30 is changed according to the mass of metal in the articles to be heated. The articles are heated to a predetermined degree of temperature. The time required for passage through the effective heating area of the induction field in the radio frequency inductance coil or coils is an average of about three seconds for small articles.

It will thus be seen that there has been provided a self-contained radio frequency induction heating apparatus wherein the intensity of the radio frequency field is selected or predetermined so that a penetration is obtained which is most advantageous for the particular mass of metal passing through the field.

Drying the outer surface of a paint coating such as by applying gas burner heat is simple, but the moisture within the paint offers difficultie and prolongs the time of baking to hours.

With the radio frequency field, the heat applied to the metal reaches the normally concealed surface of the paint, enters the paint from the inside, and travels from inside to the exterior surface of the paint. The article is heated by conduction of the heat. The heat gets directly to the interior of the coating and dries up the moisture within the coating and bakes the coated article in a few seconds. The thicker the metal, or the greater the mass, the greater the speed of the conveyor.

With the arrangement shown in Figures 1 and 2, for supporting the articles l8 while passing through the electromagnetic field, the lines of force are made to flow transversely through the largest surface area of the metal. The mechanism herein disclosed is particularly adapted for heating coated metal articles.

Figure 4 shows the radio frequency induction heating apparatus l adapted for heat treating and quenching metal articles to be case hardened. Metal articles I8, such as tool steel, are carried by the conveyor 30 past the inductance coils 3i and 35 where they are heated to a predetermined temperature and are then carried by the conveyor past a suitably directed nozzle 9i connected to a source of a quenching liquid under pressure (not shown). A cooling quenching liquid issuing from the nozzle in spray form rapidly quenches the metal directly after passing said source of heat.

Figure shows a modified quenching device comprising a tank 82 containing a cooling quenching liquid 83. The lower portion of the sprocket chain 14 of the conveyor 30 is guided by two lower pulleys 84 and by two upper pulleys 85 to cause the metal articles 18' to be lowered into the tank 82 and be submerged in the liquid for quenching purposes.

It is to be noted that sets of two pulleys B4 and sets of two pulleys 85 are employed at each position of the pulleys shown in Figure 5, and that the respective pulleys of each set are in spacedapart relation so as to permit the carrier arms [3 free passage space between them.

I have disclosed herewith a means for producing an electromagnetic field at a radio frequency because I have found this frequency to be the most eflicient for heating paint covered metal articles without any discoloration.

I have found that to prevent coatings such as paint from becoming scorched or white colored coatings from becoming discolored and yellow, that an absolutely controllable degree of heat must be applied, slightly below the safe limit, and this I have accomplished with the radio frequency induction heating mechanism herein described.

In accordance with the patent statutes I have described and illustrated the preferred embodiment of my invention, but it will be understood that various changes and modifications can be made therein without departing from the spirit of the invention as defined by the appended claims.

I claim:

1. In an apparatus for drying paint or a similar coating upon metal, comprising a casing having a heating chamber and an opening in a wall providing access to said chamber, radio frequency coils operatively mounted in said chamber, one of said coils having winding sections positioned coaxially in spaced relation and forming an open top passageway therebetween, the turns in both of said coil sections being circular and winding in the same direction, a single section coil at one side of said passageway and being positioned in spaced relation from said multi-section coil, an endless overhead travelling conveyor mounted in said casing and having a. portion thereof movably mounted above said passageway, said conveyor having inverted T-shaped carrier arms hooked thereon, each adapted to support and carry a plurality of said coated metal articles in said passageway with the respective metal surfaces positioned substantially in alinement with and transversely of the axes of all said coils, said coils being of larger diameter than said coated metal articles, means for generating radio frequency induction fields of predetermined intensity in said coil sections sufiicient to heat said metal and bake said coating, and manually adjustable means for varying the speed of said conveyor in proportion to the mass of metal of said articles being heated to cause motion of said conveyor in timed relation with the time required to heat and bake the coating on the metal articles passing through the effective areas of said induction fields, the motion of said conveyor being directed to cause said coated articles to pass said single section coil prior to passage past said multi-section coil, whereby said coatedarticles are first preheated to only a fraction of the required heat and then baked to the full predetermined heat in successive steps, said carrier arms being made of insulating material adapted for insulating the material of said conveyor from the magnetic flux in said induction fields.

2. In an apparatus for drying paint or a similar coating upon metal without discoloring said coating, comprising a casing having a heating chamber and an opening in a wall providing access to said chamber, a radio frequency induction coil operatively mounted in said chamber, said coil having winding sections positioned coaxially in spaced relation and forming an open top passageway therebetween, the turns in both coil sections running in the same direction, an endless overhead travelling conveyor having a portion thereof movably mounted above said passageway, said conveyor having inverted T-shaped carrier arms supported thereon, each adapted to support a plurality of said coated metal articles in said passageway with the respective metal surfaces held transversely of and passing through the axis of said coils, a source of electric current, means for generating a radio frequency induction field of predetermined intensity in said coil sections, and manually adjustable means for varying the speed 01 said conveyor in proportion to the mass of metal of said articles being heated to cause motion of said conveyor in timed relation with the time required to heat and dry the coated metal articles passing through the eflective area of said induction field.

JAMES J. MOREY. 

